The article presents information on pilot studies in sociology. Sociological literature distinguishes a number of techniques whose purpose is to validate research tools before proceeding to the research proper. Pilot study, pilot project, pretest, trial survey, test tube survey and pilot survey are those which are mentioned. The practices of the pilot study in Poland, as well as the uses to which its results have been put have, so far, also been very varied. This was occasioned by a number of circumstances such as, different theoretical orientations of the individual researchers and research centres, different work organization in the field research, and different demands concerning the level of the methodological precision adopted by sociologists. The conception of the in-depth pilot study resulted from the conviction that the pilot practices in Poland were not satisfactory in the new phase of the development of sociological investigations. The in-depth pilot study differs greatly from the trial survey which should be undertaken in the case of very extensive investigations. The trial survey has as its aim the preliminary assessment of the distribution of the answers, the preliminary evaluation of the hypotheses, and the like.